While the old saying "blood is thicker than water" refers more to family than anatomy, blood and water are related in a critical way.
At least 60% of the human body is water. The water and fluids we drink are absorbed by the intestines and circulated throughout the body in the form of fluids such as blood to transport hormones, chemical messengers, and nutrients to our vital organs — including the heart.
When you lose more fluids from sweating, illness, fever, or urination than you consume in food and water, you can become dehydrated. When dehydration occurs, your heart may not receive enough water and other fluids to carry out its normal functions.
Dehydration forces the heart to work harder
Dehydration negatively affects the cardiovascular system (the heart, arteries, veins, and capillaries) by increasing your blood pressure. Blood pressure is the force that circulates necessary fluids through our bodies, and the heart is the pump that maintains that pressure. The heart works constantly, pumping about 2,000 gallons of blood a day. When you are dehydrated there is less fluid for the heart to pump, so your body compensates by retaining more sodium in the blood. High sodium concentrations cause your body to close capillaries, and as the capillaries close, the pressure in your veins and arteries rises.
About that sodium
Sodium is an essential mineral for life, and is regulated by your kidneys to help control your body's fluid balance. Sodium also helps send nerve impulses and impacts muscle function.
When you're dehydrated, your body retains extra sodium in your bloodstream by pulling water into your blood vessels, increasing the total amount of blood inside them. It's like turning up the water supply to a garden hose, says the American Heart Association (AHA), and that extra pressure tires out your heart. If your body is retaining too much sodium, the extra water held in your blood can lead to noticeable symptoms such as bloating and weight gain.
Aim for 1,500 mg of sodium per day
The AHA notes that if most Americans lowered their sodium consumption to less than 1,500 mg per day, both money and lives would be saved. It has been estimated that if the U.S. population dropped its sodium intake to 1,500 mg — between ½ and ¾ teaspoon — per day, overall blood pressure could decrease by 25.6%, with an estimated $26.2 billion in health care savings. Another estimate projected that achieving this goal would reduce cardiovascular deaths by anywhere from 500,000 to nearly 1.2 million over ten years.
But reducing sodium intake is more challenging than it seems. More than 70% of the sodium we consume comes from packaged, prepared, and restaurant foods. The rest occurs naturally in food (about 15%) or is added during cooking or at the table (about 11%). So even if you never use the salt shaker, you’re probably still consuming too much sodium.
Drinking more water and eating less sodium can help reduce your risk of high blood pressure, heart attack, heart failure and stroke.
High blood pressure and dehydration
As blood becomes more concentrated from high sodium intake and dehydration, it circulates less easily. The heart compensates by squeezing harder and pumping faster. Over time, high blood pressure can overstretch or injure the blood vessel walls and speed up plaque build-up, further blocking blood flow.
High blood pressure is known as the "silent killer" because there are few symptoms. Sometimes you can feel the heart working harder in your chest where palpitations are noticeably rapid, or there is a strong or irregular heartbeat. And for people with heart disease, harder work for the heart may cause acute chest pain. Conversely, there are many noticeable symptoms and signs of dehydration, including thirst, tiredness, dizziness and lethargy, and dark yellow or strong-smelling urine. Addressing those symptoms through adequate hydration can help reduce unnecessary stress on your heart.
Low blood pressure may be dangerous, too
Orthostatic hypotension is a form of low blood pressure that happens when you stand up after sitting or lying down — and feel dizzy, light-headed, or faint. It can easily occur when you're dehydrated, because your blood volume is too low, so your blood pools in your legs and your body can't adjust its blood pressure and heart rate when you change position.
Occasional dizziness or lightheadedness may be minor — triggered by mild dehydration, low blood sugar, or overheating-- and if these symptoms happen occasionally, there's likely no cause for concern, says Mayo Clinic. But see your doctor if you have frequent symptoms or lose consciousness, even for a few seconds. It may signal serious problems.
Keep your heart healthy by staying hydrated
Water is critical for heart health. By staying well-hydrated, you're helping your heart to do its job. These tips can help you to ensure your heart (and the rest of your body) functions optimally:
- Most health experts recommend drinking eight 8-ounce glasses (64 ounces) of water, or at least half of your body weight (pounds) in ounces, every day
- Eat high water-content foods such as cucumber, lettuce, celery, tomatoes, bell peppers, cauliflower, spinach, berries, broccoli, grapefruit, grapes, and zucchini regularly
- Always drink water before and after any fitness activity